Forum Signature Bug

I am getting a signature bug today. When I try to save my changes, I get an "Invalid Image. Unable to calculate size" error. I am not even making changes to my wotlabs image, it's the only image in my signature, and I verified that it matches the 468x100 pixel maximum. Other elements of my signature also meet signature requirements.

I'd like to add onto this and sorta explain what's happening. Basically, the forum software has an issue with some HTTPS URLs on signature images. Recently WoTLabs enabled HTTPS site-wide, and thus all the signature images began to be served over HTTPS. I tried disabling HTTPS for the signature images and it worked properly.

The mystery is that it doesn't happen to all images. Imgur images which are also served over HTTPS can be embedded without problem, so it makes me think that there's some compatibility issue between some servers and Wargaming's servers.

I'm not sure who I can talk to in order to figure out what's going on. Wargaming uses the Invision Power Board software, but I'm pretty sure it's a very outdated version, and I don't know if they have technical staff for the forum.

Edit: I set up the WoTLabs server so that the signature images can be served either over HTTP or HTTPS. For the World of Tanks forum, use http:// and it should work. This isn't the ideal solution, but without someone that has server access to the forum and can help me debug this, there's not much else I can do.